The Los Pinos Formation is principally volcaniclastic, with interbedded tuffs and basalt flows.

[1] The type section is located along Los Pinos Creek, near the town of San Miguel in extreme northern New Mexico (36°57′41″N 106°10′09″W / 36.9614°N 106.1693°W / 36.9614; -106.1693).

The Cordito Member, composed mostly of rhyolitic clasts, was eroded from source areas to the east, such the Latir volcanic field and possibly another center buried beneath basalt flows of the Servilleta Formation in the Rio Grande rift.

The underlying Treasure Mountain and Masonic Park Tuffs have radiometric ages of 29.8 to 28.2 million years (Ma).

[2] It was designated the Los Pinos Member of the Hinsdale Formation, which it closely resembles, by Charles Whitman Cross and Larsen in 1935,[4] and raised to formation rank by Fred Barker in 1958.